1. The Field of the Invention
The present invention relates generally to techniques for recovery of waste heat in a power generation system, and, specifically, to heat recovery techniques for the secondary air flow system of a gas turbine engine when it is utilized as a prime mover.
2. Description of the Prior Art
Gas turbines have been used for many years in industrial applications. They have seen service as emergency power units, auxiliary power units, and more recently as a primary source of power for an industrial facility. With continuous refinement over the years, gas turbines have reached a level of efficiency at which they can provide power to a user at a less expensive rate in many instances than can be provided by the local public utility. In typical installations of this nature the gas turbine engine drives a generator or other suitable load. As the cost of fuel has increased, there has been ever greater emphasis on capturing the exhaust gases of the gas turbine and putting them to work by way of a heat recovery unit such as a steam generator. Still a further refinement has resulted in the addition to the system of a duct burner downstream of the gas turbine engine. Since the exhaust gases from the gas turbine are comprised of only approximately 20% by weight, of products of combustion, fuel added to those exhaust gases in the duct burner and then ignited, serves to more thoroughly complete the combustion process with the oxygen available to the system.
Even with such improvements as these, there has been a continuing quest for still further refinements. One typical example of a contemporary effort to achieve still greater efficiencies in heat recovery from a prime mover is found in Diesel & Gas Turbine Worldwide, Vol. XV, No. 8, October 1983, p. 48, "BOOST-FIRED CHP SYSTEM" by John Moon. According to that disclosure, the exhaust gases from a diesel engine used primarily to drive an alternator are afterburned to fire a heat exchanger and the feedwater for the heat exchanger is additionally heated in a supplementary fashion by the heated engine cooling water. While the publication appears to disclose a highly desirable concept when using diesel engines as a prime mover, it does not have any practical application to the operation of a gas turbine as a prime mover.
It was with recognition of the need which exists for still greater efficiencies and of the state of the art as generally described above, that the present invention was conceived and has now been reduced to practice.